Frequency stable magnetron



Sept. 16, 1958 P. w. CRAPUCHETTES FREQUENCY STABLE MAGNETRON 2 Sheets-Sheet 1 Filed Aug. 12, 1953 ATTORN EY P 1958 P. w. CRAPUCHETTES 2,852,720

FREQUENCY STABLE MAGNETRON Filed Aug. 12, 1953 2 Sheets-Sheet 2 lNV TO PAUL w. 1? P0 7755- ATTORN EY United States Patent 2,852,720 FREQUENCY STABLE MAGNETRON Paul W; Crapuchettes, Palo Alto, Calif., assignor to Litton Industries Inc., San Carlos, Calif., a corporation of Delaware Application August 12, 1953, Serial No. 373,761

17 Claims. (Cl. SIS-39.75)

This invention relates to magnetrons and more particularly to magnetron assemblies constructed for high frequency stability.

The operating frequency of a magnetron varies considerably under varying ambient temperatures and different energy input conditions due to the thermal expansion and contraction of the frequency determining elements. These variations occur during operation, even in the absence of permanent deformation of the structure and are correlated with the expansion characteristics of the various constituent materials. However, heretofore, the use of low expansion metals has not been possible in magnetron anode construction because of bimetallic expansion effects caused at the juncture of these materials with the other portions of the structure. Such bi-metallic effects may result from different coefiicients of thermal expansion of the materials and may result in actual rupture of certain of the connections.

In accordance with this invention a magnetron anode assembly is made of materials of low thermal coefficient of expansion, coated with highly conductive material, which permits the use of the more stable metals in magnetrons without harmful bi-metallic effects, nor the loss of efficiency due to the poor conductivity of the metals having a low temperature coefficient of expansion.

According to a feature of this invention there is provided a magnetron anode assembly including a plurality of resonator vanes interconnected by a conductive memher into a multiple resonator anode assembly in which the vanes are made up of a material having a low thermal expansion coefiicient coated with a material of a good conductivity and having a higher thermal expansion coefficient than the first named material and in which the interconnecting member is also made up principally of low thermal expansion material; the coatings of the various members being interconnected to provide a substantially continuous conductive path and low. over-all thermal expansion characteristic. The low thermal expansion material may preferably consist of molybdenum or tungsten and the coating material preferably is copper although other high conductivity materials such as silver or gold can be used.

In accordance with this invention the anode assembly may preferably be produced by the use of substantially L-shaped members having one radial part and another part extending circumferentially from one end thereof, these vane elements being made of suitably copper clad molybdenum or tungsten, for example. These elements may be assembled with the peripheral parts defining the circumference of a circle about which is mounted a ring serving to hold the elements in rigid position. The ends of the circumferential parts are then brazed to the ends of adjacent radial parts. This construction provides only one brazed connection in each resonator, as compared with two in the usual structure, reducing the attenuation, which normally occurs at the brazing points, by one half. Furthermore, the larger circumferential area of these vanes may be strongly brazed or otherwise secured to the 2,852,720 Patented Sept. 16, 1958 bodyring portion. In addition, the usual strapping rings required in magnetrons for stable operation are also preferably made of low expansion metal clad with a good conductive metal in a manner similar to that of the vanes.

A suitable stock for producing the magnetron vanes may be tungsten or molybdenum sheet which is first coated with a nickel coating by a suitable process, after which the copper cladding is secured to the nickel coated surface. Applicant has found that the particular method of cladding tungsten or molybdenum set forth herein produces material suitable for use in magnetron structures and capable of withstanding the rigorous and wide temperature variations to which it is subjected without appreciable damage to the magnetron itself.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which:

Figure 1 is an end view of a magnetron anode assembly incorporating the features of this invention;

Figure Z is a sectional view of the anode assembly of Fig. 1 taken along the line 22 of Fig. 1;

Figure 3 is a detailed drawing illustrating in sectional View one of the vanes of Fig. 1;

Figure 4 is a diagrammatic illustration of an alterna tive magnetron construction in accordance with the principles of this invention, and

Figure 5 is a sectional view of line 55 of that figure.

Turning now to the drawing, the main anode body ring is shown at 1. Mounted within this ring is a plurality of radial vane elements 2. Each of these radial vane elements 2 has a radial part 3 and circumferential part 4. The vane elements are arranged to extend radially from a point near the center of the circle defined by the circumferential portions 4. The circumferential parts 4 are arranged in contact with the outer ends of the outer radial parts 3, so that the contiguous circumferential parts substantially define a circle having a radius substantially the same as the inner radius of ring 1. The portions then of the successive vanes 2 which are in contact are brazed together and brazed or otherwise suitably secured to body portion ring 1. The L-shaped vane members are so constructed as to be substantially similar except that in alternate ones of the vanes the notches for the strapping rings 5 and 6 are on opposite sides of the vanes at different depths as can be clearly seen in Fig. 2. Furthermore two of these vanes 2 are made somewhat different in order to terminate one of the resonators, as indicated at 7. These two vanes each have the L-portions made one half the normal circumferential range of the sector shaped resonators so that they may be placed together at the single center point. Also, the output resonator 8 may be defined by the first and last elements 2 without requiring an additional vane therefor. Preferably an opening is provided as indicated at 8 in an anode ring 1, for output coupling to an output wave guide or the like.

' Each of the vane elements as shown in Fig. 3 is comprised of a center portion 9 made of low thermal expansion material suchas molybdenum or tungsten and is coated on its outer surfaces with a high conductivity metal as indicated at 10, such as cooper. To obtain a firm bond between the copper and the low thermal expansion material, a thin coating of nickel 16 may be provided. This is shown in the drawing by the heavy black line and indi- Fig. 4 taken along the cated by the legend in Fig. 3. Preferably also the inner jig. The brazing compound is then applied at the contacting edges of the vanes 2 and the assembly is heated to braze these parts together. Strapping rings 5 and 6 are then applied and brazed to the'altern'ate vane elements 2. The anode ring 1 may then be supported in a suitable jig and the circular vane assembly brazed to the inner surface thereof. A copper tube 11, preferably relatively thin, may be secured to the outer periphery of ring'l for mounting the anode asembly and connecting it to the other portions of the magnetron tube. For simplicity of illustration the remaining structure of the magnetron has been omitted.

While the L-shaped anode assembly illustrated in Figs. 1-3 is preferred, a modified form of anode resonator assembly in accordance with the principles of this invention may be constructed in the manner shown in Figs. 4 and 5. In this arrangement the anode vanes 12 are shown as straightelements of copper clad molybdenum stock which may be brazed to the copper lining 13 of a molybdenum body ring 14. If desired a copper body cylinder may be provided for connecting the anode assembly to other portions of the tube. It will be realized that the illustration particularly in Figs. 4 and S is simply diagrammatic and does not indicate the relative thickness of the various metals used, nor the proper relative dimensions thereof.

In an actual magnetron made to operate in a range of 9060 megacycles and constructed substantially in accordance with the illustration shown in Figs. l, 2 and 3, remarkable frequency stability was achieved over a relatively wide temperature variation. In fact, when the temperature was varied 110 C. the frequency shift of only 2.1 megacycles per second was noted, whereas in the conventional magnetron at the same frequency range made entirely of copper, a frequency shift of about megacycles per second occurs for the same temperature change.

Considerable experimentation was found necessary in order to obtain a suitable covered molybdenumor tungsten stock which would achieve the necessary stability within the temperature operating range of the magnetron. Ordinary copper plating on molybdenum was found to separate and blister under operating conditions and so ruin the tube for proper operation. A method for producing stock for construction of the magnetron is as follows:

The molybdenum or tungsten is first cleaned chemically in the usual manner, the base stock material is then flushed with nickel in a low pH solution containing chlorine and fluorine negative ions. The flashed stock is then plated with nickel to a thickness of approximately .0002 inch after which the plated stock is heated to flow the nickel on the stock metal in an inert hydrogen atmosphere at a temperature of approximately 1350 C. just long enough completely to flow the nickel. To this nickel clad stock material the copper may be applied in a number of dilferent ways.

One method of applying the copper is to flash the coated metal with copper and plate this flashed material to a thickness of approximately .0002 inch with copper, after which the assembly is heated sufficiently to melt the copper into the nickel. This is then replated with copper to the desired thickness. This thickness may be made sufficient to take care of machining or polishing, if this is desired.

Another method is simply to braze the copper sheet to the nickel clad material with suitable solders.

A third method consists in rolling a sheet of copper onto the nickel clad material and reducing the sheet of copper in thickness, the pressure of rolling being sufiicient to produce a cold welding of the copper to the nickel at the bond. This cold welded stock is then heated in an inert atmosphere, such as hydrogen, to a temperature to produce a sintering condition of the copper and the nickel.

It is clear that instead of copper, silver or gold can be used as a low conductive material if desired.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by Way of example and not as a limitation to the scope of my invention, as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. A magnetron anode assembly comprising a plurality of resonator vanes, and a conductive member interconnecting said vanes to complete a plurality of individual resonators, said vanes each comprising a material of low thermal expansion coefiicient having a coating of a material of good conductivity and a higher thermal expansion coefiicient, said member comprising a material of low thermal expansion, said coatings being intimately joined to produce an anode assembly having a low thermal expansion and good conductivity.

2. A magnetron anode assembly according to claim 1, wherein said vanes are each made with a radial extending vane part, and a circumferentially extending part, said circumferentially extending parts serving as the circumferential walls of the respective resonators.

3. A magnetron assembly accordingto claim 2, wherein said circumferentially extending parts are brazed to the outer ends of adjacent radialparts to provide continuous conductive walls for said resonators.

4. A magnetron assembly according to claim 1, wherein said low conductivity metal is molybdenum.

5. A magnetron assembly according to claim 4, wherein said material of good conductivity is copper.

6. A magnetron assembly according to claim 5, further comprising an intermediate coating of nickel bonding said copper coating to said molybdenum.

7. A magnetron anode assembly according to claim 1, further comprising strapping rings of low conductivity metal of low thermal coefiicient of expansion.

8. A magnetron anode assembly according to claim 7, wherein said strapping rings are coated with a metal of high conductivity.

9. A magnetron anode assembly comprising a plurality of vane elements, said vane elements each having similar circumferentially extending parts and a radially extending part, means for positioning said vanes with said circumferentially extending parts forming substantially a circular periphery, the outer ends of radially extending parts being in contact with adjacent ends of circumferentially extending parts, and means for conductively connecting the contacting portions whereby a plurality of sectorshaped resonators is formed.

10. A magnetron assembly according to claim 9, wherein each of said vane elements comprises a central body portion of a metal of relatively low thermal coeflicient of thermal expansion of relatively high resistance, and a coating on said body of a metal of relatively good conductivity but having higher coeflicient of thermal ex pansion than said body portion.

11. A magnetron assembly according to claim 10, wherein said body portion is molybdenum and said coating is of copper.

12. A magnetron according to claim 11, wherein said means for connecting the contacting portions consist of a braze between the adjacent copper coatings.

13. An anode assembly according, to claim 9, further comprising a substantially solid ring of conductive material having an inner radius substantially of the same radius as that of said periphery fastened to the outer peripheral surface of said vane assembly. e 1

14. A resonator structure for an ultrahigh frequency electron discharge device, comprising a cavity resonator forming substantially enclosed resonant space, the wall of said resonator comprising a metal of relatively low thermal expansion coeflicient, a coating on the inner surface of said wall of material of good conductivity and higher coeflicient of thermal expansion than said wall,

said coating being intimately joined to said first metal to produce a resonator having low thermal expansion and good conductivity.

15. A resonator structure according to claim 14, wherein said low conductivity metal is molybdenum.

16. A resonator structure according to claim 15, wherein said material of good conductivity is copper.

17. A resonator structure according to claim 16, further comprising an intermediate coating of nickel bonding said copper coating to said molybdenum.

References Cited in the file of this patent UNITED STATES PATENTS Heising July 5, 1949 Espersen Jan. 3, 1950 Stinchfield Apr. 8, 1952 Burrack Oct. 7, 1952 Barr Dec. 2, 1952 

